Performance of porous capacitor electrodes

ABSTRACT

Fabricating a capacitor includes forming conduits in a porous layer of material. The porous layer of material has particles that each includes a dielectric on a core. The formation of the conduits causes a portion of the dielectric to convert from a first phase to a second phase. The method also includes removing at least a portion of the second phase of the dielectric from the porous layer of material.

FIELD

The invention relates to electrochemical devices. In particular, theinvention relates to electrodes in capacitors.

BACKGROUND

Increasing the surface area of the anodes in many types of capacitorscan lead to an increased capacitance. One approach to increasing thesurface area is to form the anode from powder particles that are fusedtogether such that pores are positioned between different fusedparticles. These pores provide the desired increase in the surface areaof the anode; however, these capacitors have suffered from an inabilityto get both the capacitance and the delivered to stored energy ratio(electrical porosity) above desired target levels. For the abovereasons, there is a need for improved capacitor anodes.

SUMMARY

A method of fabricating a capacitor includes forming conduits in aporous layer of material. The porous layer of material has particlesthat each includes a dielectric on a core. The formation of the conduitscauses a portion of the dielectric to convert from a first phase to asecond phase. The method also includes removing at least a portion ofthe second phase of the dielectric from the porous layer of material.

A capacitor has an anode with an active layer having both pores andconduits. The active layer includes particles that each has a dielectricon a core. The pores are located between the particles. A medium in theconduits is in direct physical contact with the dielectric on differentparticles.

Another version of a capacitor includes an anode with an active layerthat has both pores and conduits. The conduits are arranged on theactive layer in a periodic two-dimensional pattern.

Another version of a capacitor includes an anode with an active layerhaving both pores and conduits. The conduits extend from a surface ofthe active layer into the active layer. An average width of the conduitsis more than 2 times an average width of the pores.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A through FIG. 1D illustrate the construction of an anode for usein a capacitor. FIG. 1A is a sideview of an anode that is suitable foruse in the capacitor. The anode includes conduits extending into anactive layer.

FIG. 1B is a cross-section of the anode 10 shown in FIG. 1A taken alongthe line labeled B in FIG. 1A.

FIG. 1C is a cross-section of the anode 10 shown in FIG. 1A taken alongthe line labeled C in FIG. 1A.

FIG. 1D is a cross section of a portion of the anode shown in FIG. 1Athrough FIG. 1C. FIG. 1D shows more details of the relationship betweena conduit and the components of the active layer. The conduit extendspart way into the active layer.

FIG. 2A is a sideview of a cathode that is suitable for use in thecapacitor.

FIG. 2B is a cross-section of the cathode shown in FIG. 2A taken alongthe line labeled B in FIG. 2A.

FIG. 3A is a cross section of an electrode assembly where anodes arealternated with cathodes.

FIG. 3B is a schematic diagram of a capacitor that includes theelectrode assembly of FIG. 3A positioned in a capacitor case.

FIG. 3C is a cross section of a capacitor illustrating the positioningof the electrode assembly relative to the capacitor case.

FIG. 3D is a sideview of an interface between an anode and a cathodethat are adjacent to one another in the capacitor of FIG. 3B.

FIG. 4A is a cross section of a portion of the anode shown in FIG. 1Athrough FIG. 1C. A conduit extends through an active layer to anunderlying current collector.

FIG. 4B is a cross section of a portion of the anode shown in FIG. 1Athrough FIG. 1C. A conduit extends through the entire anode.

FIG. 5A through FIG. 5H illustrate a method of generating an anode foruse in a capacitor constructed according to FIG. 1A through FIG. 3D.FIG. 5A is a cross section of a sheet of material that has fusedparticles on a current collector. An anode precursor will be extractedfrom the sheet of material at a later stage of the method.

FIG. 5B is a cross section of the sheet of material of FIG. 5A afterdielectrics are formed on the fused particles so as to provide fusedparticles that each have the dielectric on a core.

FIG. 5C is a cross section of the sheet of material of FIG. 5B after aconduit is formed in the sheet of material. The formation of the conduitcan convert a first phase of the dielectric to a second phase of thedielectric that is located in the conduit.

FIG. 5D is a cross section of the sheet of material of FIG. 5C after atleast a portion of the second phase of the dielectric is removed fromthe sheet of material.

FIG. 5E is a cross section of the sheet of material of FIG. 5D after thedielectric is formed on exposed cores of the fused particles.

FIG. 5F illustrates extraction of anode precursor from the sheet ofmaterial of FIG. 5C, FIG. 5D, or FIG. 5E.

FIG. 5G is a topview of a portion of a sheet of material having a laserpathway with multiple different tracks.

FIG. 5H illustrates tracks selected so as to provide an edge of an anodewith the desired shape.

FIG. 6 is a schematic diagram of a defibrillation system that includesan Implantable Cardioverter Defibrillator (ICD) that employs one or morecapacitors constructed according to FIG. 1A through FIG. 5H.

DESCRIPTION

The capacitor has an anode with an active layer that includes fusedparticles. Voids between the fused particles provide pores through whichan electrolyte can travel through the active layer. In some instances,these active layers are formed using techniques such as sintering of apowder. It has been found that the capacitance of such a capacitorincreased by decreasing the average size of the powder particles thatare subsequently fused together. However, decreasing the size of thepowder particles results in narrower and more tortuous pore pathways.The small width of the pores combined with the tortuous nature of theirpath through the active layer generates resistance to the movement ofelectrolyte through the pores. This reduced movement of the electrolytethrough the pores reduces the delivered to stored energy ratio(electrical porosity) of the capacitor.

The active material includes conduits that can extend from a surface ofthe active layer into the active layer. The average width of theconduits can be on the order of 2-20 times the average width of thepores. Additionally, the pores can be open to the interior of theconduits. Accordingly, the electrolyte can easily flow in and out of theconduits where it can enter and/or exit from the pores through theconduits. As a result, the conduits provide a larger pathway from theexterior surface of an active layer to pores that are deep within theactive layer. The larger pathway reduces the resistance of the activelayer to the movement of electrolyte through the active layer andaccordingly increases the delivered to stored energy ratio (electricalporosity). As a result, the conduits make it possible for the activelayer to have the higher capacity associated with narrow and tortuouspores and also to have an elevated electrical porosity.

FIG. 1A through FIG. 1D illustrate the construction of an anode for usein a capacitor. FIG. 1A is a sideview of an anode 10 that is suitablefor use in the capacitor. FIG. 1B is a cross-section of the anode shownin FIG. 1A taken along the line labeled B in FIG. 1A. FIG. 1C is across-section of the anode shown in FIG. 1A taken along the line labeledC in FIG. 1A.

The anode 10 includes one or more active layers 12 on a currentcollector 14. The illustrated anode 10 includes the current collector 14positioned between active layers 12. Suitable current collectors 14include, but are not limited to, foils, meshes, and screens. FIG. 1Athrough FIG. 1C show a portion of the current collector 14 extendingbeyond the one or more active layers 12. The exposed portion of thecurrent collector 14 is optional and can be used for making electricalconnections to the anode 10. Conduits 16 extend into the active layers12. The conduits 16 are shown with circular cross sections althoughother configurations are possible.

FIG. 1D is a cross section of a portion of the anode 10 shown in FIG. 1Athrough FIG. 1C. The cross section is taken through a conduit 16 andshows more details of the active layer 12 construction than is shown inFIG. 1A through FIG. 1C. The active layers 12 include particles that arefused together (fused particles 18). For instance, the active layers 12can include sintered powder particles. As a result, a single fusedparticle 18 shown in FIG. 1D may represent a single particle of a powderor can represent two or more particles of powder that are fusedtogether.

The fused particles 18 include, consist of, or consist essentially of alayer of a dielectric 20 on a core 22. The cores 22 can be electricallyconducting and one or more of the cores 22 can be in direct physicalcontact with the current collector 14. Additionally, the fusion of thefused particles 18 provides an electrical pathway between differentcores 22. As a result, the cores 22 are in electrical communication withthe current collector 14.

In some instances, the dielectric 20 is an anode metal oxide and thecore 22 is an electrical conductor such as an anode metal. The anodemetal oxide can be an oxide of an anode metal included in the core 22.Suitable anode metals include, but are not limited to, aluminum,tantalum, magnesium, titanium, niobium, and zirconium. Many anode metaloxides can exist in more than one phase within the same material state(solid, liquid, gas, plasma). For instance, an anode metal oxide such asaluminum oxide can be in a solid first phase called the boehmite phase(Al₂O₃) or a second phase called alpha phase corundum oxide (α-Al₂O₃)that is also a solid.

The active layer 12 includes pores 24 that result from the voids betweenadjacent fused particles 18 and that are present throughout the activelayer 12. The pores 24 have non-uniform diameters and/or non-uniformcross sections and follow tortuous pathways through the active layer 12.A suitable porosity for portions of the active layer 12 that do notinclude any conduits 16 include, but are not limited to, porositygreater than 1%, 2% or 5% and/or less than 10%, 20% or 30%. An averagewidth for the pores is greater than 0.1 μm, 1 μm, or 5 μm, and/or lessthan 100 μm, or 200 μm.

The conduits 16 extend from an exterior surface of an active layer 12into the active layer 12 toward the current collector 14. The conduits16 are fabricated after fusing the particles. The conduits 16 can befabricated in a way that cuts through individual fused particles 18. Asa result, the portion of the fused particles that define the conduits 16can be smooth or substantially smooth. The dielectric 20 on the fusedparticles 18 defines the walls of the conduits 16. Accordingly, a mediumlocated in the conduits 16 can be in direct physical contact with thedielectric 20. For instance, in a completed capacitor, an electrolyte inthe conduits 16 can be in direct physical contact with the dielectric20.

In some instances, the conduits 16 are fabricated to have a uniform orsubstantially uniform diameter and/or width along the depth of theconduit 16. In some instances, the length of the conduits 16 isperpendicular or substantially perpendicular to a surface of the currentcollector 14 and/or to a surface of the active layer 12. Additionally,the conduits 16 can be straight or substantially straight along theirlength. Accordingly, the conduits 16 can follow a less tortuous pathwaythrough an active layer 12 than is followed by the pores 24.

FIG. 2A is a sideview of a cathode 26 that is suitable for use in thecapacitor. FIG. 2B is a cross-section of the cathode 26 shown in FIG. 2Ataken along the line labeled B in FIG. 2A. The cathode 26 includes alayer of cathode metal oxide 28 over a layer of a cathode metal 30.Suitable cathode metals 30 include, but are not limited to, aluminum,titanium, and stainless steel. Although not illustrated, the cathodemetal 30 can be layer of material on a substrate. For instance, thecathode metal 30 can be a titanium or titanium nitride coating on asubstrate such as a metal and/or electrically conducting substrate.Examples of suitable substrates include, but are not limited to,aluminum, titanium, and stainless steel substrates. The cathode metaloxide 28 can be formed on the cathode metal 30 by oxidizing the cathodemetal 30 in air. The cathode metal 30 can be the same as the anode metalor different from the anode metal. In some instances, the cathode metal30 and the anode metal are both aluminum. As illustrated in FIG. 2B, insome instances, the cathode metal oxide 28 surrounds the cathode metal30. For instance, the cathode metal oxide 28 is positioned over theedges and faces of the cathode metal 30.

The anodes 10 and cathodes 26 are generally arranged in an electrodeassembly 32 where one or more anodes 10 are alternated with one or morecathodes 26. For instance, FIG. 3A is a cross section of an electrodeassembly 32 where anodes 10 are alternated with cathodes 26. The anodes10 and cathodes 26 can be constructed according to FIG. 1A through FIG.2B. A separator 34 is positioned between anodes 10 and cathodes 26 thatare adjacent to one another in the electrode assembly 32. The electrodeassembly 32 typically includes the anodes 10 and cathodes 26 arranged ina stack or in a jelly roll configuration. Accordingly, the cross sectionof FIG. 3A can be a cross section of an electrode assembly 32 havingmultiple anodes 10 and multiple cathodes 26 arranged in a stack.Alternately, the cross section of FIG. 3A can be created by winding oneor more anodes 10 together with one or more cathodes 26 in a jelly rollconfiguration. However, as the anodes 10 become more brittle due toincreased surface area, it may not be practical or possible to form ajellyroll configuration. Suitable separators 34 include, but are notlimited to, kraft paper, fabric gauze, and woven for non-woven textilesmade of one or a composite of several classes of nonconductive fiberssuch as aramids, polyolefins, polyamides, polytetrafluoroethylenes,polypropylenes, and glasses.

The electrode assembly 32 is included in a capacitor. For instance, FIG.3B is a schematic diagram of a capacitor that includes the electrodeassembly 32 of FIG. 3A positioned in a capacitor case 36. Although notillustrated, the one or more anodes 10 in the electrode assembly 32 arein electrical communication with a first terminal 38 that can beaccessed from outside of the capacitor case 36. The one or more cathodes26 in the electrical assembly are in electrical communication with asecond terminal 40 that can be accessed from outside of the capacitorcase 36. In some instances, the one or more anodes 10 include or areconnected to tabs (not shown) that provide electrical communicationbetween the one or more anodes 10 and the first terminal 38 and the oneor more cathodes 26 include or are connected to tabs (not shown) thatprovide electrical communication between the one or more cathodes 26 andthe second terminal 40. The capacitor can include one or more electricalinsulators (not shown) positioned as needed to prevent shorts-circuitswithin the capacitor.

FIG. 3C is a cross section of a capacitor illustrating the positioningof the electrode assembly 32 relative to the capacitor case 36. Thefirst terminal 38 and the second terminal 40 are not shown in FIG. 3C.The illustrated electrode assembly 32 includes anodes 10 and cathodes 26stacked such that anodes 10 are alternated with cathodes 26 andseparators 34 are positioned between adjacent anodes 10 and cathodes 26.The upper side of the capacitor case 36 is curved. In order to make bestuse of the space that is available in the case, the electrode assembly32 is configured to conform to the interior of the capacitor case 36. Asa result, a portion of the anodes 10 and/or cathodes 26 have taperededges that allow these electrodes to be positioned adjacent to thecurved portion of the capacitor case 36. As is evident in FIG. 3C, theability to shape the electrode edges increases the packing efficiency ofthe electrodes within the capacitor case. Further, the conduits may makeit possible to use a thicker anode. The use of thicker anodes can alsoimprove packing efficiency because fewer anodes would be needed in thecapacitor case. When the disclosed anodes are included in an ImplantableCardioverter Defibrillator (ICD), a suitable thickness for the anodesmay include a thickness greater than 100 μm or 400 μm and/or less than500 μm or 1000 μm. Additionally or alternately, different electrodeswithin the electrode assembly 32 can have different sizes. For instance,the electrodes closer to the top of the capacitor case 36 shown in FIG.3C can have a smaller width (labeled w in FIG. 3C) or diameter.

FIG. 3D is a sideview of an interface between an anode 10 and a cathode26 that are adjacent to one another in the capacitor of FIG. 3B. Theillustration in FIG. 3D is magnified so it shows features of the anode10 and cathode 26 that are not shown in FIG. 2A and FIG. 2B. Forinstance, the surface of the cathode 26 optionally includes cathodechannels 44 that extend into the cathode metal 30 so as to increase thesurface area of the cathode metal 30. Suitable cathode channels 44include, but are not limited to, pores, trenches, tunnels, recesses, andopenings. The cathode metal oxide 28 can be positioned on the surface ofthe cathode metal 30. When the cathode metal 30 includes cathodechannels 44, the cathode metal oxide 28 can be positioned in the cathodechannels 44. The cathode metal oxide 28 can fill the cathode channels 44and/or cathode oxide channels 46 can extend into the cathode metal oxide28.

An electrolyte 48 is in contact with the separator 34, the anode 10 andthe cathode 26. The electrolyte 48 can be positioned in the pores 24 ofthe active layers 12. The components of the anode 10 can be positionedon the cores 22 such that the cores 22 do not directly contact theelectrolyte 48. For instance, the dielectric 20 and the currentcollector 14 can prevent direct contact between the cores 22 and theelectrolyte 48. In some instances, the dielectric 20, an oxide, and thecurrent collector 14 can prevent direct contact between the cores 22 andthe electrolyte 48. For instance, the oxide can form on the surface ofthe core when the electrolyte and core come into contact while anelectrical potential is applied to the cores.

When the cathode metal 30 includes cathode oxide channels 46, theelectrolyte 48 can be positioned in the cathode oxide channels 46. Theelectrolyte 48 can be a liquid, solid, gel or other medium and can beabsorbed in the separator 34. The electrolyte 48 can include one or moresalts dissolved in one or more solvents. For instance, the electrolyte48 can be a mixture of a weak acid and a salt of a weak acid, preferablya salt of the weak acid employed, in a polyhydroxy alcohol solvent. Theelectrolytic or ion-producing component of the electrolyte 48 is thesalt that is dissolved in the solvent.

A capacitor constructed according to FIG. 3A through FIG. 3D can be anelectrolytic capacitor such as an aluminum electrolytic capacitor, atantalum electrolytic capacitor or a niobium electrolytic capacitor. Anelectrolytic capacitor is generally a polarized capacitor where theanode metal oxide serves as the capacitor dielectric and the electrolyte48 effectively operates as the cathode.

It has been found that the capacitance of a capacitor constructedaccording to FIG. 3A through FIG. 3D can be increased by decreasing theaverage size of particles that are subsequently fused together. Forinstance, when the fused particles 18 are generated by fusing powderparticles, the capacitance of the capacitor constructed can be increasedby decreasing the average size of powder particles. However, thedecreasing size of the particles that are subsequently fused together isalso associated with narrower and more tortuous pore pathways. The smallwidth of the pores 24 combined with the tortuous nature of their paththrough the active layer 12 generates resistance to the movement ofelectrolyte 48 through of the pores 24. Reduced movement of electrolyte48 through the pores 24 reduces the delivered to stored energy ratio(electrical porosity). The conduits 16 help to overcome this issue. Forinstance, the average width of the conduits 16 can be on the order to2-20 times the average width of the pores 24. Additionally, as isevident from FIG. 1D, the pores 24 are open to the interior of theconduits 16 along the depth of the conduit 16. Accordingly, theelectrolyte 48 can easily flow through of the conduits 16 where it canenter and/or exit from the pores 24 through the conduits 16. As aresult, the conduits 16 provide a larger pathway from the exteriorsurface of an active layer 12 to pores 24 that are deep within theactive layer 12. The larger pathway reduces the resistance of the activelayer 12 to the movement of electrolyte 48 in an out of the active layer12 and accordingly increases the delivered to stored energy ratio(electrical porosity). The conduits 16 permit the capacitor to havedelivered to stored energy ratio (electrical porosity) greater than0.85:1 or 0.90:1 and/or less than 0.90:1 or 0.95:1. In application suchas Implantable Cardioverter Defibrillator (ICD), it is desirable for thedelivered to stored energy ratio (electrical porosity) to be at or above0.90 for packaging efficiency and to improve the battery life perbattery volume due to a reduction in the amount of stored energy neededfor the battery to charge the capacitor to deliver the same outputenergy.

One or more variable selected from the group consisting of the width,average width, diameter and average diameter of a conduit 16 can be morethan 0.1 μm, 1 μm, or 50 μm and/or less than 200 μm, 500 μm, or 1000 μm.Additionally or alternately, one or more variable selected from thegroup consisting of the width, average width, diameter and averagediameter of the conduits 16 can be more than 1, 2, 5, or 10 times theaverage width of the pores 24 and/or less than 20, 50, 100, or 200 timesthe average width of the pores 24 times the average width of the pores24. The aspect ratio or average aspect ratio of the conduits 16 can begreater than 5:1, 6:1, or 8:1 and/or less than 11:1, or 20:1. As will bedescribed in more detail below, the conduits 16 can be formed by laserdrilling. The upper limit for the aspect ratio of laser drilled conduits16 is generally less than 11:1. Accordingly, aspect ratios less than11:1 may currently be the practical upper limit for conduits 16 althoughlater developments may make higher aspect ratios practical. Lower aspectratios can also be used but are generally associated with a reduction insurface area of the active layer 12.

Increasing the average density of the porosity openings across thesurface of the active layer 12 can increase the uniformity ofelectrolyte flow in and out of the active layer 12 across the activelayer 12. However, increasing the number of conduits 16 can also reducethe surface area of the active layer 12 and accordingly reduce thecapacitance. A suitable average density of the conduits across thesurface of the active layer 12 includes, but is not limited to, anaverage density greater (ratio of active layer surface area that is notoccupied by an opening to a conduit:active layer surface area that isoccupied by the opening to a conduit) than 1:1, 20:1, or 50:1 and/orless than 200:1, 500:1, or 1000:1. The conduit density that is desiredcan be a function of the conduit depth. For instance, deeper conduitscan permit the conduit density to be reduced.

The conduits 16 can be arranged in a two-dimensional periodic pattern.For instance, FIG. 1A shows the conduits 16 arranged in hexagonalpattern. Arranging the conduits 16 in a two-dimensional pattern canincrease the uniformity of electrolyte flow in and out of the pores 24across the active layer 12. Other examples of suitable patterns for theconduits 16 include, but are not limited to, square and triangular.Other arrangements for the conduits 16, including random arrangements,can be used; however, random or pseudorandom patterns may result in anuneven flow of electrolyte in and out of the pores 24 across the activelayer 12.

Although FIG. 1D shows a conduit 16 extending part way through thethickness of the active layer 12, the conduits 16 can extend through anactive layer 12 to the underlying current collector 14 as shown in FIG.4A. Alternately, the conduits 16 can extend through the anode and/orthrough both active layers 12 and the current collector as shown in FIG.4B. The active layers 12 have a thickness that is labeled T in FIG. 4Aand is measured in a direction perpendicular to a surface of the currentcollector 14. When the conduit 16 extends part way through the thicknessof the active layer 12, a suitable depth for the conduits 16 includes,but is not limited to, depths that are greater than 50% and/or less than100% of the thickness of the active layer 12.

FIG. 5A through FIG. 5H illustrate a method of generating an anode 10for use in a capacitor constructed according to FIG. 1A through FIG. 3D.FIG. 5A is a cross section of a sheet of material 50 that has fusedparticles 18 on a current collector 14. An anode precursor will beextracted from the sheet of material 50 at a later stage of the method.Suitable methods of generating the sheet of material 50 include, but arenot limited to, sintering of powder on the current collector 14.Sintering includes pressing and/or compacting the powder without meltingthe powder to the point of liquefaction. Heat may or may not be appliedduring the sintering process.

In some instances, the powder used in generating the sheet of material50 can have a constant diameter or width. However, in other instances,the powder used in generating the sheet of material 50 can have avariety of different diameters or widths. Since smaller particles canfit into the pores 24 between larger particles, a variety of differentpowder sizes can increase the surface area of the active layer 12.Suitable diameters or widths or average diameters or average widths forthe powder can be greater than 2 μm, 4 μm, or 5 μm, and/or less than 6μm, 7 μm, or 10 μm. Suitable powders include, but are not limited to,aluminum, tantalum, magnesium, titanium, niobium, and zirconium.

The dielectrics 20 can be formed on the fused particles 18 in the sheetof material 50 of FIG. 5A so as to provide the sheet of material 50 ofFIG. 5B. FIG. 5B is a cross section of the sheet of material 50. Whenthe fused particles 18 are an anode metal, the dielectrics 20 can be anoxide of the anode metal. An example of a suitable method of forming theanode metal oxide dielectric 20 on the fused particles 18 includesmechanisms that convert existing anode metal to anode metal oxide. Inthese mechanisms, a portion of the fused particles 18 is converted to anoxide that serves as the dielectric 20 while another portion of thefused particles 18 is not converted and serves as the core 22. Asuitable method for converting an existing anode metal to an anode metaloxide includes, but is not limited to, anodic oxidation. In anodicoxidation, the sheet of material 50 is placed in an electrolytic bathwhile a positive voltage is applied to the sheet of material 50. Thethickness of the layer of anode metal oxide can be increased byincreasing the applied voltage. When the anode metal is aluminum, anodicoxidation forms a layer of the first phase (boehmite phase) of aluminumoxide (Al₂O₃) on a layer of aluminum. In one example of anodicoxidation, the anode metal oxide is formed by placing the sheet ofmaterial 50 in citric acid while a positive voltage of 400-550 volts isapplied to the sheet of material 50 for a period of time. Additionallyor alternately, the electrical current that results from the appliedvoltage can be monitored and the sheet of material 50 can be removedfrom the electrolytic solution in response to the electrical currentfalling below a threshold exit leakage current.

The conduits 16 are formed in the fused particles 18 in the sheet ofmaterial 50 of FIG. 5B so as to provide the active layers 12 shown inthe sheet of material 50 of FIG. 5C. Suitable methods of forming theconduits 16 include, but are not limited to, laser drilling. However,laser drilling the conduits 16 can cause melted portions of the sheet ofmaterial 50 to solidify in a conduit and close the conduit 16.Additionally or alternately, portions of the sheet can redeposit in theconduits 16 and/or on a surface of the active layer during the laserdrilling process. The presence of these materials in the conduits 16and/or on the surfaces of the active layer can be reduced by using apulsed laser beam. The short pulse durations that are possible withpulsed lasers can provide very high peak powers for moderately energeticpulses. The increased peak power can provide vaporization of the fusedparticles 18 and/or current collector 14 during the laser drillingprocess. This vaporization can eject the material from the conduits 16through the top of the conduit 16. Since the material is ejected fromthe sheet of material 50, the material is not available to re-solidifyor re-deposit the conduit 16.

In some instances, the duration of the pulse is greater than 0 s, or afemtosecond (10⁻¹⁵ s) and/or less than a microsecond (10⁻⁶ s). In oneexample, the duration of the pulse is greater than 100 femtoseconds andless than 900 femtoseconds. The time between pulses is inversely relatedto the pulse frequency. Suitable pulse frequencies can be greater than 0Hz, or 100 Hz, and/or less than 2000 kHz. In one example, the pulsefrequency is in a range of 200 kHz to 600 kHz. In some instances, theduration of the pulse is greater than 0 s, or a femtosecond (10⁻¹⁵ s)and/or less than a microsecond (10⁻⁶ s) and the pulse frequency isgreater than 0 Hz, or 100 Hz, or 100 kHz and/or less than 2000 kHz.

The power density of the laser beam at the sheet of material 50 can beat a level that a single pulse elevates the temperature of the sheet ofmaterial 50 above the boiling point of the anode metal and vaporizes theanode metal. In some instances, power density of the laser beam is suchthat at least a portion of the sheet of material 50 that is illuminatedby the laser reaches the boiling point of the dielectric 20, core 22,and/or current collector 14 and vaporizes a portion of dielectric 20,core 22, and/or current collector 14 in a period of time less than orequal to the duration of one pulse when the illuminated portion of thesheet of material 50 is at temperature (23° C. or 25° C.) before thepulse. In an example where the anode metal is aluminum, the pulseduration is 820 femtoseconds, the pulse frequency is 400,000 pulses persecond, and the laser beam has a power density 7.99×10¹¹ W/cm² at thesurface of the sheet of material 50. Suitable power densities include,but are not limited to, power densities greater than 0 W/cm², 1×10¹¹W/cm², or 2×10⁵ W/cm² and/or less than 9×10¹¹ W/cm², or 2×10⁵ W/cm¹².The combination of elevated power densities and reduced pulse durationsreduces the amount of heat transferred to the sheet of material 50.

The path of the laser beam across the face of the sheet of material 50can be controlled by electronics and/or software. The electronics and/orsoftware can move the laser beam relative to the sheet of material 50and/or the sheet of material 50 relative to the laser beam. Accordingly,the conduits 16 can be drilled sequentially in the sheet of material 50.In some instances, all or a portion of the conduits 16 can be partiallydrilled and the laser can later return to the partially drilled conduits16 to further drill the partially drilled conduits 16. In theseinstances, the laser can return to the partially drilled conduits 16 oneor more times until the conduits 16 have reached the desired depth.

When the dielectric 20 is an oxide, the high heat transfer that occursduring the laser drilling process can convert the dielectric 20 to aless desirable second phase 54 that is present on the surface(s) in theinterior conduits 16. For instance, when the dielectric 20 is aluminumoxide, the laser drilling can convert the aluminum oxide from thedesirable first phase called boehmite (Al₂O₃) to the undesirable secondphase 54 called alpha phase corundum oxide phase (α-Al₂O₃). The corundumoxide is undesirable and can increase leakage current and deformation.Further, the corundum oxide is stable and very difficult to convert backto a suitable aluminum oxide phase.

The less desirable second phase 54 of the dielectric 20 is removed fromthe sides of the conduits 16 in the sheet of material 50 of FIG. 5C soas to provide the sheet of material 50 of FIG. 5D. Suitable methods forremoving the second phase 54 of oxide include, but are not limited to,widening processes such as etching. Suitable etches include, but are notlimited to, chemical and electrochemical processes such as wet etches.During these processes, the etch can be selected such that thedielectrics 20 on the fused particles 18 acts as a mask that protectsthe underlying cores 22 from the etchant. In one example of a wideningprocess, widening of the conduits 16 includes immersing at least aportion of the sheet of material 50 in an electrolyte solution thatincludes, consists of, or consists essentially of a chloride or nitratesuch as aluminum nitrate. Additional examples of suitable methods forwidening of the preliminary channels 52 and/or additional details aboutthe above methods of widening preliminary channels 52 can be found inU.S. patent application Ser. No. 05/227,951, filed on Feb. 22, 1972,granted U.S. Pat. No. 3,779,877, and entitled “Electrolytic Etching ofAluminum Foil;” U.S. patent application Ser. No. 06/631,667, filed onJul. 16, 1984, granted U.S. Pat. No. 4,525,249, and entitled “Two StepElectro Chemical and Chemical Etch Process for High Volt Aluminum AnodeFoil;” U.S. patent application Ser. No. 11/972,792, filed on Jan. 11,2008, granted U.S. Pat. No. 8,535,527, and entitled “ElectrochemicalDrilling System and Process for Improving Electrical Porosity of EtchedAnode Foil;” U.S. patent application Ser. No. 10/289,580, filed on Nov.6, 2002, granted U.S. Pat. No. 6,858,126, and entitled “High CapacitanceAnode and System and Method for Making Same;” and U.S. patentapplication Ser. No. 10/199,846, filed on Jul. 18, 2002, granted U.S.Pat. No. 6,802,954, and entitled “Creation of Porous Anode Foil by Meansof an Electrochemical Drilling Process;” each of which is incorporatedherein in its entirety.

Removing the second phase 54 of the dielectric is optional. Removing thesecond phase 54 of the dielectric can be done during subsequentprocesses. An example of a suitable process for removing the secondphase 54 of the dielectric is the oxide phase extraction is described inmore detail below.

The process of removing the second phase 54 of the dielectric can leavecores 22 within the conduits 16 exposed to the interior of the conduits16 as shown in FIG. 5D. Accordingly, additional dielectric 20 can beformed in the interior of conduits 16 so as to provide the sheet ofmaterial 50 of FIG. 5E. For instance, additional dielectric can beformed on the interior walls of the conduits 16 in FIG. 5D. As anexample, when the cores 22 are an anode metal and the dielectric 20 isan anode metal oxide, at least the portion of the cores 22 that areexposed to the contents of the conduits 16 can be converted from thecore material to the oxide of the core material. A suitable method forconverting an existing anode metal to an anode metal oxide includes, butis not limited to, anodic oxidation. In anodic oxidation, the sheet ofmaterial 50 is placed in an electrolytic bath while a positive voltageis applied to the sheet of material 50. The thickness of the layer ofanode metal oxide can be increased by increasing the applied voltage.The dielectric 20 formed in the interiors of the conduits 16 can be thefirst phase of the dielectric. For instance, when the anode metal isaluminum, anodic oxidation forms a layer of the first phase of aluminumoxide (boehmite, Al₂O₃) on a layer of aluminum. In one example of anodicoxidation, the anode metal oxide is formed by placing the sheet ofmaterial 50 in citric acid while a positive voltage of 400-550 volts isapplied to the sheet of material 50 for a period of time. Additionallyor alternately, the electrical current that results from the appliedvoltage can be monitored and the sheet of material 50 can be removedfrom the electrolytic solution in response to the electrical currentfalling below a threshold exit leakage current.

Forming additional dielectric 20 in the interior of conduits 16 isoptional. The additional dielectric 20 can be formed on the interiorwalls during subsequent processes. An example of a suitable subsequentprocess for forming additional dielectric 20 on the interior walls ofthe conduits 16 includes, but is not limited to, an aging process thatis described in more detail below.

One or more anode precursors can be extracted from the sheet of material50 of FIG. 5C, or FIG. 5D or FIG. 5E. Accordingly, a portion of thesheet of material 50 becomes the anode(s). Suitable methods of removingan anode precursor from the sheet of material 50 include, but are notlimited to cutting the anode precursor(s) out of the sheet of material50. A suitable method of cutting the anode precursor(s) out of the sheetof material 50 include mechanical cutting method such as die cuttingwhere the anode precursor is punched or stamped from a sheet of material50 using a mechanical die. Another suitable method of cutting the anodeprecursor(s) out of the sheet of material 50 includes no-contact cuttingmethods such as laser cutting of the anode precursor.

Laser cutting may provide an increase in yield and efficiency whencompared with mechanical cutting methods. Laser cutting of the sheet ofmaterial 50 can cause melted portions of the sheet of material 50 tosolidify and stay on the resulting anode precursor. Alternately,portions of the sheet can redeposit on the resulting anode precursorduring the laser cutting process. These excess materials can be reducedby using a pulsed laser beam. The short pulse durations are possiblewith pulsed lasers can provide very high peak powers for moderatelyenergetic pulses. The increased peak power can provide vaporization ofthe sheet of material 50 during the laser cutting process. Thisvaporization can eject the material from any recess or trench created inthe sheet of material 50 through the top of the sheet of material 50.Since the material is ejected from the sheet of material 50, thematerial is not available to re-solidify or re-deposit on the sheet ofmaterial 50.

In some instances, the duration of the pulse is greater than 0 s, or afemtosecond (10⁻¹⁵ s) and/or less than a microsecond (10⁻⁶ s). In oneexample, the duration of the pulse is greater than 100 femtoseconds andless than 900 femtoseconds. The time between pulses is inversely relatedto the pulse frequency. Suitable pulse frequencies can be greater than 0Hz, or 100 Hz, and/or less than 2000 kHz. In one example, the pulsefrequency is in a range of 200 kHz to 600 kHz. In some instances, theduration of the pulse is greater than 0 s, or a femtosecond (10⁻¹⁵ s)and/or less than a microsecond (10⁻⁶ s) and the pulse frequency isgreater than 0 Hz, or 100 Hz, or 100 kHz and/or less than 2000 kHz. Thepulse duration and/or frequency can be the same or different as thepulse duration and/or frequency used during laser drilling.

The power density of the laser beam at the sheet of material 50 can beat a level that a single pulse elevates the temperature of the sheet ofmaterial 50 above the boiling point of the anode metal and vaporizes theanode metal. In some instances, power density of the laser beam is suchthat at least a portion of the sheet of material 50 that is illuminatedby the laser reaches the boiling point of the anode metal and vaporizesin a period of time less than or equal to the duration of one pulse whenthe illuminated portion of the sheet of material 50 is at temperature(23° C. or 25° C.) before the pulse. In an example where the cores 22include or consist of aluminum as an anode metal, the pulse duration is820 femtoseconds, the pulse frequency is 400,000 pulses per second, andthe laser beam has a power density 7.99×10¹¹ W/cm² at the surface of thesheet of material 50. Suitable power densities include, but are notlimited to, power densities greater than 0 W/cm², 1×10¹¹ W/cm², or 2×10⁵W/cm² and/or less than 9×10¹¹ W/cm², or 2×10⁵ W/cm¹². In some instances,one, two, or three of the parameters selected from the group consistingof pulse duration, frequency, and power density are the same duringlaser cutting as during laser drilling. The combination of elevatedpower densities and reduced pulse durations reduces the amount of heattransferred to the sheet of material 50. However, adjusting theseparameters may not be sufficient to address an increase in deformationthat can result from using laser cutting of the anodes rather thanstamped or punched cutting of the anodes.

The path of the laser beam across the face of the sheet of material 50during cutting can be controlled by electronics and/or software. Theelectronics and/or software can move the laser beam relative to thesheet of material 50 and/or the sheet of material 50 relative to thelaser beam. FIG. 5F illustrates use of a laser 56 to cut anodeprecursors 58 out of a sheet of material 50 constructed according toFIG. 5C, FIG. 5D, or FIG. 5E. In some instances, the same laser used todrill the conduits 16 is used to remove the anode precursors 58 from thesheet of material 50. In FIG. 5F, the solid lines and the dashed linesthat show the outline of an anode precursor 58 in the sheet of material50 represent the laser beam pathway during the process of cutting theanode precursor 58 from the sheet of material 50.

The inventors have found that tuning the characteristics for the laserbeam path across the sheet of material 50 can also reduce the leakageand deformation to or even below the levels associated with stamping orpunching of anodes. For instance, the rate at which the beam is scannedacross the sheet of material 50 can be tuned. Faster scan rates reducethe amount of energy that is absorbed by the anode precursor. In someinstances, the laser beam is scanned across the sheet of material 50 ata rate greater than 0 mm/sec, 100 mm/sec, or 600 mm/sec, and/or lessthan 900 mm/sec, or 1100 mm/sec.

Reducing the spot size can also reduce the amount of thermal energytransferred to the sheet of material 50. Suitable spot sizes include,but are not limited to, spot having a diameter or major axis greaterthan 10 microns, 30 microns and/or less than 50 microns, or 150 microns.Additionally or alternately, the spot size can be selected to producespot overlaps less than 100%. A spot is the area of the sheet ofmaterial 50 illuminated by the laser beam during a pulse. Spot overlapis the overlap of a spot with the spot provided by the previous pulse.Suitable spot overlaps include spot overlaps greater than 70%, or 90%and/or less than 100%. The spot size can be selected to provide theselevels of spot overlap when combined with the above scan rates and pulsefrequencies.

Increasing the beam scan rate can reduce the depth that the laser beamcuts into the sheet of material 50. As a result, multiple passes of thelaser beam along a pathway may be necessary in order to completely cutthe anode precursor out of the sheet of material 50. This result isevident in the pathway labeled P FIG. 2G. The pathway includes dashedlines that indicate where the laser beam has cut into the sheet ofmaterial 50 without cutting through the sheet of material 50. Thepathway also includes solid lines that indicate the portion of the anodeprecursor outline where the laser beam has cut through the sheet ofmaterial 50. Additionally, the arrow labeled A indicates the traveldirection travel for the laser beam relative to the anode precursor. Atthe start of the laser cutting, the laser beam may be incident on theanode metal oxide. Once the laser beam has cut through the anode metaloxide, the laser beam is incident on the anode metal.

The need for multiple passes of the laser beam in order to cut throughthe sheet of material 50 means that each location along the beam pathwayis not exposed to the laser beam energy for a pass interval. The passinterval can be the time between passes of the laser beam and/or can bethe period of time that passes between each point along the pathwaybeing exposed to the laser beam. Suitable pass intervals include, butare not limited to, pass intervals more than 0.1 seconds per pass and/orless than 3 seconds per pass. In some instances, the pass interval isselected such that more than 5, or 10 and/or less than 100 passes of thelaser beam around the entire outline of the anode precursor are requiredto completely extract an anode precursor from the sheet of material 50.

The laser pathway can includes multiple different tracks. FIG. 5G is atopview of a portion of a sheet of material 50. A portion of a laserpathway on the sheet of material 50 is labeled P. The laser pathwayincludes a first track 59 represented by dashed lines and a second track60 represented by solid lines. The first track 59 represents the trackthat the laser follows during a pass along the laser pathway. The secondtrack 60 represents the track that the laser follows during a differentpass along the laser pathway. The first track 59 has a width labeled wand the second track 60 has a width labeled W. When the first track 59and the second track 60 are followed by the same laser or by lasers withthe same spot size, the width of the first track 59 will be the same orabout the same as the width of the second track 60.

The second track 60 is offset from the first track 59 by a distancelabeled OS in FIG. 5G. The amount of offset can be selected such thatthe second track 60 partially overlaps the first track 59 as shown inFIG. 5G. The use of partially overlapping tracks while laser cutting theanode precursor widens the trench that the laser forms in the sheet ofmaterial 50 to a width larger than the spot diameter. The cutting of awider trench can reduce the amount of thermal energy that is applied topreviously formed surfaces in the trench. The track overlap percentagecan be the overlap distance divided by the width of the overlappedtrack. Suitable track overlap percentages include, but are not limitedto, track overlap percentages greater than 25% or 30% and/or less than50% or 75%. The offset distance can be a function of spot size. Forinstance, when the spot size has a diameter of 40 microns, a suitableoffset distances can be any distance between 0 and 40 microns such as 10to 30 microns.

In some instances, the different tracks extend around the perimeter ofthe anode and/or surround the perimeter of the anode. For instance, theentire length of the laser pathway shown FIG. 5F can include two tracksthat partially overlap as shown in FIG. 5G. In other words, the laserpathway of FIG. 5G can represent the laser pathway of any straightportion of the laser pathway shown FIG. 5F. Accordingly, the laser cantrace all, or substantially all, of the anode perimeter along one trackand later trace all, or substantially all, of the anode perimeter alonganother track that partially overlaps the prior track as describedabove. Alternately, different tracks can partially overlap along one ormore portions of the anode perimeter but completely overlap along one ormore other portions of the anode perimeter.

Although the laser pathway in FIG. 5G is illustrated as having twotracks, the laser pathway can include a single track or more than twotracks. During the laser cutting process, a track can be followed onceor more than once. For instance, when a laser pathway includes twotracks as is shown in FIG. 5G, the laser can alternate between differenttracks on subsequent passes. As an example, the laser can follow thefirst track 59, the second track 60, the first track 59, the secondtrack 60, and so on until the trench extends through the sheet ofmaterial 50 and the anode precursor is extracted from the sheet ofmaterial 50.

The tracks can be selected so as to provide the edges of the anode withthe desired taper and/or shape as described in the context of FIG. 3C.For the purpose of illustration, FIG. 5H illustrates tracks selected soas to provide an anode with a linearly tapered edge although othershapes are possible. FIG. 5H shows four different images that eachincludes a cross section of the same part of the sheet of material 50.In each image, a laser is positioned over the sheet of material 50. Eachof the images represents a different track. The arrows indicate wherethe light is incident on the sheet of material 50 as the laser is movedalong the track associated with that image. The sheet of material 50shows the portion of the sheet of material 50 that remains after thelaser have removed a portion of the sheet of material 50. As is evidentfrom the rightmost image, the tracks have been selected such that thelaser cuts through the sheet of material 50 and also provides an anodewith a tapered edge. Although the illustrated taper is a linear taper,the taper need not be linear.

In some instances, the anode precursor is fabricated using one, two,three, four, five or six parameters selected from the group consistingof a laser pulse duration, pulse frequency, power density, scan rate,pass interval, and pass number where the laser pulse duration is 400femtoseconds, the laser pulse frequency is 400 kHz, the power density is7.99×10¹¹ W/cm², the scan rate is 720 mm/sec, the pass interval is 0.25s, and the pass number is 60.

The inventors have found that using a laser to extract one or more anodeprecursors from the sheet of material 50 can convert at least a portionof the first phase of the dielectric 20 to the second phase of thedielectric. For instance, using a laser to cut a sheet of material 50having fused particles 18 with aluminum cores and the boehmite phase ofaluminum oxide (Al₂O₃) as the dielectric can convert the boehmite phaseof aluminum oxide to the second phase of the aluminum oxide(alpha-corundum oxide, α-Al₂O₃). This conversion is believed to be aresult of the heat generated during the laser cutting process. As aresult, the conversion primarily occurs at and/or near the edge of theanode precursor. As noted above, the second phase of the anode metaloxide is often undesirable. For instance, the second phase of the anodemetal oxide can be more electrically conductive than the first phase ofthe anode metal oxide. As an example, the alpha corundum oxide (α-Al₂O₃)phase of aluminum oxide has properties of a semiconductor. As a result,the alpha phase corundum oxide (α-Al₂O₃) is not suitable for use as adielectric and is accordingly associated with undesirably high levels ofleakage and deformation. However, alpha phase corundum oxide (α-Al₂O₃)is very stable and is difficult to convert back into the boehmite phaseof aluminum oxide. While adjustments to the laser cutting parametersdisclosed above can partially address the leakage and deformationassociated with the this conversion from the first phase of the anodemetal oxide to the second phase of the anode metal oxide, an oxideextraction phase discussed in more detail below can further reduce theleakage and deformation caused by this conversion.

The one or more anode precursors constructed having fused particles 18according to FIG. 5C, or FIG. 5D or FIG. 5E are included in a capacitorprecursor according to FIG. 3A through FIG. 3C. For instance, one ormore of the anode precursors are combined with one or more separators 34and one or more cathodes so as to form an electrode assembly 32 with thecomponents arranged as disclosed in the context of FIG. 3A through FIG.3C. The electrode assembly 32 is placed in a capacitor case 36 alongwith the electrolyte. Any electrical connections needed for operation ofthe capacitor precursor are made before and/or after the electrodeassembly 32 is placed in the capacitor case 36 and the capacitor case 36is sealed.

The capacitor precursor can optionally be put through an aging phase.The aging phase can be configured to form an anode metal oxide on anyanode metal that is exposed at the at the walls of the conduits 16 asshown in FIG. 5C or FIG. 5D and/or at the edges of the one or more anodeprecursors in the capacitor and/or at the edges of the anode precursoras a result of laser cutting an anode precursor such as anode precursorsconstructed according to FIG. 5C or FIG. 5D, or FIG. 5E. The agingprocess can use water in the electrolyte to form the anode metal oxide.The phase of the anode metal oxide formed during the aging phase is notnecessarily the same as the first phase of the anode metal oxide and/orthe second phase of the anode metal oxide. For instance, when the anodemetal is aluminum, the anode metal oxide formed during the aging phaseis not the first phase (boehmite phase) but is similar.

Suitable methods for aging the capacitor precursor include, but are notlimited to, holding the capacitor at an elevated temperature whilecharged. For instance, in some instances, aging includes holding thecapacitor at a temperature greater than 50° C. or 70° C. and/or lessthan 100° C. or 200° C. for a time greater than 2 hours, or 20 hours,and/or less than 50 hours or one hundred hours while charged to avoltage greater than 50 V, or 200 V and/or less than 600 V or 800 V. Inone example, aging includes holding the capacitor at about 85° C. for 24to 36 hours while charged to about 400 V.

An oxide phase extraction can be performed on the capacitor precursor61. The oxide phase extraction can include an oxide removal stage thatremoves all or a portion of the second phase of the anode metal oxidefrom the anode precursor and/or from the portion of the sheet ofmaterial 50 that serves as the anode precursor. Accordingly, the oxideremoval stage can remove the second phase of the anode metal oxide inthe anode precursor of FIG. 5C and/or that is positioned at the edges ofthe anode precursor as a result of laser cutting an anode precursor suchas an anode precursor constructed according to FIG. 5C or FIG. 5D, orFIG. 5E.

In some instances, the oxide phase extraction moves all or a portion ofthe second phase of the anode metal oxide from the anode precursor intothe electrolyte. The oxide phase extraction can be performed such thatthe first phase of the anode metal oxide remains intact or remainssubstantially intact. The oxide phase extraction can also include anoxide restoration stage that forms the anode metal oxide on exposedanode metal and/or on areas where the anode metal oxide is thin. Thephase of the anode metal oxide formed during the oxide restoration stagecan be the first phase of the anode metal oxide. As a result, the oxiderestoration stage can restore the first phase of the anode metal oxidein places where the first phase and/or second of the anode metal oxidewas removed or damaged during the oxide removal stage. Suitable methodsfor the oxide restoration stage can be the same or similar to themethods used in the aging phase.

An example oxide phase extraction includes one or more cycles. Eachcycle can include the oxide removal stage followed by the oxiderestoration phase. When the oxide phase extraction includes multiplecycles, the cycles can be repeated in series. An example oxide phaseextraction includes a high temperature stage that acts as an oxideremoval stage followed by a low temperature stage and a charging stage.The low temperature stage can be performed between the high temperaturestage and the charging stage. The high temperature stage can beconfigured to move all or a portion of the second phase of the anodemetal oxide from the anode precursor and into the electrolyte. The lowtemperature stage can be configured to form the first phase of the anodemetal oxide on any anode metal that becomes exposed during the hightemperature stage. The charging stage causes a current surge through theanode precursor that reforms the anode metal oxide. For instance, thecharging stage can form the first phase of the anode metal oxide on theanode precursor from oxygen in the electrolyte. Accordingly, the lowtemperature stage and the charging stage together can serve as an oxiderestoration stage.

An example of a single cycle of the oxide phase extraction includes ahigh temperature stage where the capacitor precursor is exposed to atemperature T₁ for a time period P₁; a low temperature stage where thecapacitor precursor is exposed to a temperature T₂ for a time period P₂;and a charging stage where the capacitor precursor is charged to V₁ anddischarged. The cycle of the oxide phase extraction can be performed Ntimes.

Examples of suitable T₁ include, but are not limited to, T₁ greater than45° C., or 50° C. and/or less than 90° C. or 100° C. In some instances,prolonged exposure of the capacitor to temperatures above 90° C. candamage one or more components of the capacitor. Examples of suitable P₁include, but are not limited to, P₁ greater than 0.5 hours and/or lessthan 2 days. The variables T₁ and P₁ can be a function of materialsand/or configuration. Additionally, the value of P₁ can be a function ofT₁. Exposure of a capacitor precursor 61 to increased temperatures forprolonged periods of time can damage the capacitor precursor components.As a result, as T₁ increases, it is generally desirable to reduce thevalue of P₁. For example, when T₁ is above 85° C., P₁ can be less than 2hours but when T₁ is below 50° C., P₁ can be more than 1 day.

Examples of suitable T₂ include, but are not limited to, T₂ greater than35° C., or 45° C. and/or less than 50° C. or 70° C. Examples of suitableP₂ include, but are not limited to, P₂ greater than 10 minutes and/orless than 100 minutes or one day. In some instances, T₁ is higher thanT₂ but P₁ is longer than P₂. Examples of suitable V₁ include, but arenot limited to, V₁ greater than 200 V, 400V and/or less than 500V or600V. Examples of suitable N include, but are not limited to, N greaterthan 0, 1, or 8 and/or less than 15, 25, or 35.

An example of the oxide phase extraction includes any one, any two, anythree, any four, any five, or any six features selected from the groupconsisting of T₁ greater than 45° C., or 50° C. and/or less than 90° C.or 100° C., P₁ greater than 0.5 hours and/or less than 2 days, T₂greater than 35° C., or 45° C. and/or less than 50° C. or 70° C., P₂greater than 10 minutes and/or less than 100 minutes or one day, V₁greater than 200 V, 400V and/or less than 500V or 600V. In someinstances, this oxide phase extraction is performed for a number ofcycles, N, greater than 0, 1, or 8 and/or less than 15, 25, or 35.

When the cores 22 include aluminum as the anode metal and the firstphase of the anode metal oxide is the boehmite phase of aluminum oxide,an example of a cycle the oxide phase extraction includes a hightemperature stage where the capacitor precursor is placed in a 90° C.(+/−5° C.) oven for 1 hour (+/−5 min); a low temperature stage where thecapacitor precursor is placed in a 37° C. (+/−5° C.) oven for 30 minutes(+/−5 min); a charging stage where the capacitor precursor is charged to422.5 Volts and discharged. To execute the oxide phase extraction, thiscycle of the oxide phase extraction can be performed once orsequentially repeated for 1 or more cycles to 35 or fewer cycles. Thetotal number of cycles performed can be a function of the capacitorresponse to the preceding cycles. For instance, performance ofadditional cycles can be optional or skipped once the time needed tocharge the capacitor after a cycle is less than a threshold. In oneexample, the threshold is 5% of the time needed to charge the capacitorbefore the cycle.

The exact number of cycles needed can be a function of the properties ofthe sheet of material 50 and the thermal effect of laser cutting on theedge. As a result, the number of cycles that are performed can bevariable. For example, the time needed to charge the capacitor precursorcan be measured after each cycle. The measured charge time can becompared to a charge time threshold. If the charge time for cycle jexceeds the threshold, then an additional cycle can be performed. Whenthe charge time for cycle j falls below the threshold, additional cyclesare not performed. For instance, the threshold can be a percentage ofthe time needed to charge the capacitor after the immediately precedingcycle. In one example, the threshold is 5% of the time needed to chargethe capacitor before the cycle.

Completion of the oxide extraction phase provides the anode andcapacitor of FIG. 3A through FIG. 3C. Accordingly, the capacitor isready for use in the desired application and/or for resale.

The above capacitors can be used in medical devices such as anImplantable Cardioverter Defibrillator (ICD). FIG. 6 is a schematicdiagram of a defibrillation system that includes an ImplantableCardioverter Defibrillator (ICD) that employs one or more capacitorsconstructed as disclosed above. The defibrillation system includes leadlines 62 connected to electrodes 64 in contact with the heart. Althoughthe defibrillation system is shown with two electrodes 64, thedefibrillation system may include three or more electrodes 64 and/orthree or more lead lines. The specific positions of the electrodes 64relative to the heart 66 is dependent upon the requirements of thepatient.

The defibrillation system also includes a processing unit 68. The leadlines 62 provide electrical communication between the processing unit 68and the electrodes 64. The processing unit 68 is also in electricalcommunication with one or more capacitors constructed as disclosedabove.

The processing unit 68 receives power from a battery 72. The processingunit 68 can place the battery 72 in electrical communication with theone or more capacitors 70. For instance, the processing unit 68 cancause the battery 72 to charge the one or more capacitors 70.Additionally, the processing unit 68 can place the one or morecapacitors 70 in electrical communication with the lead lines 62. Forinstance, the processing unit 68 can cause the one or more capacitors tobe discharged such that electrical energy stored in the one or morecapacitors is delivered to the heart through all or a portion of theelectrodes 64. The processing unit 68, the battery 72 and the one ormore capacitors 70 are positioned in a case 84.

During operation of the defibrillation system, the defibrillation systememploys output from the lead lines 62 to monitor the heart and diagnosewhen defibrillation shocks should be provided. When the processing unit68 identifies that defibrillation shocks are needed, the processing unit68 provides the heart with one or more defibrillation shocks. To providea defibrillation shock, the processing unit 68 employs energy from thebattery 72 to charge the one or more capacitors 70. Once the one or morecapacitors are charged, the processing unit 68 causes these capacitorsto be discharged such that energy stored in the capacitors is deliveredto the heart through all or a portion of the electrodes 64 in the formof defibrillation shocks. During the defibrillation shocks, thedefibrillator requires that one or more pulses be delivered from thebattery 72 to the one or more capacitors. Each pulse is generallyassociated with a defibrillation shock. The duration of each pulse isgenerally about 8 to 12 seconds with the pulses separated by a delaytime that is based on how fast the battery charges the capacitor anddetermining the appropriate point to provide the defibrillation shock.

Suitable processing units 68 can include, but are not limited to, analogelectrical circuits, digital electrical circuits, processors,microprocessors, digital signal processors (DSPs), computers,microcomputers, or combinations suitable for performing the monitoringand control functions. In some instances, the processing unit 68 hasaccess to a memory that includes instructions to be executed by theprocessing unit 68 during performance of the control and monitoringfunctions.

The sequence of events disclosed above for forming an anode can beperformed in a sequence other than the disclosed sequence. For instance,the oxide phase extraction can be performed on an anode precursor(s)before the capacitor is assembled.

Although the above methods of forming an anode have been disclosed inthe context of a capacitor, the above oxide phase extraction can also beapplied to the fabrication of anodes, cathodes, positive electrodes,and/or negative electrodes in batteries.

Although the above methods of forming the capacitor makes use of anodeshaving edges tapered by laser cutting, the corresponding cathodes canalso include tapered edges as shown in FIG. 3A. The edges of thecathodes can be shaped using a laser as described above and/or by othershaping mechanisms.

Although the electrode assembly 32 is disclosed in the context of anodesalternating with cathodes other electrode arrangements are possible asis known in the capacitor and battery arts.

Although not shown above, portions of the anode current collector 14that are exposed while forming oxide at one or more points in thefabrication process may also be converted to an oxide of the anodecurrent collector 14 material. These regions of oxide in the anodecurrent collector 14 can prevent the electrolyte from coming into directcontact with the electrically conducting portions of the anode currentcollector 14.

Other embodiments, combinations and modifications of this invention willoccur readily to those of ordinary skill in the art in view of theseteachings. Therefore, this invention is to be limited only by thefollowing claims, which include all such embodiments and modificationswhen viewed in conjunction with the above specification and accompanyingdrawings.

1. A capacitor, comprising: an anode that includes an active layerhaving both pores and conduits, the conduits being arranged in aperiodic two-dimensional pattern.
 2. The capacitor of claim 1, whereinthe periodic two-dimensional pattern is a hexagonal pattern.
 3. Thecapacitor of claim 1, wherein an average width of the conduits is morethan 2 times an average width of the pores.
 4. The capacitor of claim 1,wherein the conduits each has a length and the length of the conduits isstraight.
 5. The capacitor of claim 1, wherein the active layer includesparticles that each has a dielectric on a core and the pores are locatedbetween the particles.
 6. The capacitor of claim 5, wherein anelectrolyte in the conduits is in direct physical contact with thedielectric on different particles.
 7. A capacitor, comprising: an anodethat includes an active layer having both pores and conduits, the activelayer including particles that each has a dielectric on a core with thepores being located between the particles, and a medium in the conduitsbeing in direct physical contact with the dielectric on differentparticles.
 8. The capacitor of claim 7, wherein an average width of theconduits is more than 2 times an average width of the pores.
 9. Thecapacitor of claim 7, wherein the conduits each has a length and thelength of the conduits is straight.
 10. A capacitor, comprising: ananode that includes an active layer having both pores and conduits, theconduits extending from a surface of the active layer into the activelayer, and an average width of the conduits is more than 2 times anaverage width of the pores.
 11. The capacitor of claim 10, wherein anaverage width of the pores is less than 10 μm.
 12. The capacitor ofclaim 1, wherein the conduits each has a length and the length of theconduits is straight.
 13. A method of fabricating a capacitor,comprising: forming conduits in a porous layer of material, the porouslayer of material having particles that each includes a dielectric on acore, the formation of the conduits causing a portion of the dielectricto convert from a first phase to a second phase; and removing at least aportion of the second phase of the dielectric from the porous layer ofmaterial.
 14. The method of claim 13, wherein the first phase isboehmite and the second phase is alpha phase corundum oxide.
 15. Themethod of claim 13, wherein at least a portion of the converted secondphase is located in the conduits.
 16. The method of claim 17, whereinremoving the second phase of the dielectric includes removing the secondphase from within the conduits.
 17. The method of claim 16, whereinremoving the second phase from within the conduits includes widening ofthe conduits.
 18. The method of claim 16, further comprising: formingthe dielectric in an interior of the conduits after removing the secondphase from within the conduits.
 19. The method of claim 16, wherein thedielectric formed in the interior of the conduits is the first phase ofthe dielectric.
 20. The method of claim 13, wherein forming the conduitsincludes laser drilling of the conduits.